Electric-furnace voltage control



March 13, 1928. 7 1,662,149

A. E. GREENE ELECTRIC FURNACE VOLTAGE CONTROL Original Filed Jan. 3.1913 3 Sheets-Sheet 1 March 13, 1928.

A. E. GREENE ELECTRIC FURNACE VOLTAGE CONTROL Original Filed Jan. 3,1913 3 Sheets-She 2 I] I luv enrofi March 13, 1928. 1,662,149

A. E. GREENE ELECTRIC FURNACE VOLTAGE CONTROL 7 Original Filed Jan. 3,1913 3 Sheets-Sheet 3 Patented Mar. 13, 1928.

UNITED STATES PATENT OFFICE.

ALBERT E. GREENE, OF MEDINA, WASHINGTON.

ELECTRIC-FURNACE VOLTAGE CONTROL.

Continuation of applications Serial No. 207,966, filed January 3, 1913;Serial No. 157,931, filed March 28, 1917; and Serial No. 322,298, filedSeptember 8, 1919. This application filed May 23, 1923. Serial Mypresent invention relates to the voltage control apparatus for electricfurnaces and processes for operating the same. My invention relatesparticularly to certain kinds of low voltage transformers for use inconjunction with standard voltage transformers furnishing current to theelectrodes of electric furnaces-and to the combination of these specialtransformers with standard transformers in connection with electricfurnaces for changing, controlling and regulating the voltage applied tothe furnace electrodes.

In my co-pending applications, Serial N 207,966, filed January 3, 1913,and Serial No. 157,931, filed March 28, 1917, and Serial No. 322,298,filed Sept. 8, 1919, I have described and claimed certain improvementsin the combination of transformers and elec- 0 tric furnaces, and mypresent invention re lates to improvements of the same kind. Mypresent-application is a continuation of those applications abovementioned.

I-Ieretofore in making provision for chang ing the voltage on electricfurnaces it has been customary to have the power transformersconstructed in a special manner with taps or other connections so thatthe voltage applied to the furnaceelectrodes can be varied to meet. theparticular requirements. This has been done in a number of cases. Forexample, the primary windings of the transformers are provided with tapsso that the number of turns connected between-the power lines may bechanged and therefore the induced secondary voltage may becorrespondinglv varied. Or in other instances where three transformershave their primaries connected to a three-phase power line, provisionhas been made to change the connections of the primaries from delta-tostar and thus change the induced secondary voltage applied to theelectrodes. In other cases the secondary windings of the transformersare provided with coils which may be connected in either series orparallel relation as more particularly described in my application forPatent 157,931, filed March 28, 1917.

\Vhere large furnaces are used the transformers must be of large powercapacity.

The arrangements just mentioned involve the construction of very specialtransformers and such transformers are usually very xpensive and requireconsiderable time for their. construction and they are also made forsuch special voltage as not to be serviceable for general power work.

But my present invention has for one of its objects the combination of aspecial low voltage transformer and astandard power transformeriin orderto provide a simple means of changing voltage applied to the furnaceelectrodes. This special low voltage transformer is a voltage regulatingtransformer with independent or connected primary and secondary windingsdesigned to take current from the secondary side of the powertransformers and to add to or subtract from the voltage furnished bythose standard power transformers. This combination has many advantagesand it makes possible the use of standard power transformers which takepower from a high voltage power line on their primary side and furnishcurrent at a standard low voltage such as 110 volts or 220 volts orother standard low voltage.

In-tlie operation of electric arc steel furnaces for melting andrefining steel the range of voltage required between the electrodes of athree-electrode, three-phase furnace ranges from about -80 volts up toabout 140 volts and sometimes lower or higher than these voltages. Powertransformers are usually equipped-with secondary windings to furnish 110or 220 volts. In case of the standard power transformer furnishing 110volts, my present invent-ion contemplates using a special low voltagetransformer to raise or lower this 110 volts to the desired limits. Forexample, I may use a special transformer which will add volts to the 110volts and thereby provide 140 volts between each pair of the three-phaseconductors leading to the electrodes. And I may. also operate this sametransformer to subtract 30 volts from the 110 volts and thus supply 80volts to the electrodes. I may provide this special low voltagetransformer, which may be called a booster transformer, withintermediate taps so that a voltage less than 30 volts may be added toor subtracted from the secondary voltage supplied by the standard powertransformer. For example, I may proylde the booster transformer withtaps and windings so that it will boost the voltage from 110 to 120, orfrom 110 to 130, that is by adding 10 voltsor by adding 20 volts to thestandard 110 volts secondary voltage. Also .I may reverse the directionof the currentthrough primary winding of the booster transiornacrwithout change of secondaryconnection so as to subtr-act- 10 volts or 20volts from the secondary voltage of 110. These are special features ofmy present invention.-

My invention contemplates also constructing and combining a boostertransformer so as to have its secondary windings in series with-theconductors leading to the furnace electrodes, and at the same time haveits primary windings connected in one way or another between thesecondary terminals of the standard voltage transformers. vThus forexample, my invention contemplates furnishing power to three electrodesof a threephase arcfurnace from powertransformers connected to give 110volts between'secondary lines. That is 110 volts between each p'airofth'e three conductors leading to the furnace ele'ctrode=, and in thiscombination I' insert a booster transformer so that each secondary?winding of the booster transformer-is? in series with a conductor .to anelectrode, and each primary winding of the booster transformer would beconnected to a'se'condary terminal of the standard power transformers.At

One feature of my present invention relates to't-he means of changingthe voltage of the booster transformer and this ma be accomplished byproviding the secon arywindings of the booster transformers with 'two ormore coils which may operate in 'either ieries or parallel relation; orthe booster -'transformer may "be likewise constructed "with two or moreprimary coils which niay ibe='operated in either series or parallelrelation, or taps may be provided either on the primary or the secondarywindings of each phase; or the primary windings may be connected betweenthe standard low voltage terminals of the power transformers in star ordelta relation so as to vary the induced voltage in the boostertransformer.

My invention further contemplates the use of switches so as to changethe direction of -the current through the windings of the boostertransformer; that'is my invention contemplates either adding to orsubtracting from voltage the standard voltage between the powerlrai'isformcr terminals.

In one modification, my invention contenipla'teso constructing} thewindings of the booster transformer, either the primary or the secondarywindings,"-so that a portion of the winding can be connected in parallelwith another portion or so that these two portions-foam be connected .inseries, this change being accomplished by the means of a double throwswitch. This change in connection from parallel to series of the saidportions of windings would result in a change in the induced voltagethrough these portions of the primary winding or would change thesecondary terminal voltage of the booster transformer; if the portionsare on the secondary side. In either case the improvements maltea verycliicient arrangement of windings for voltage change. This specialfeature of my invention is not limited to ordinary transformers but maybe used in induction furnaces for varying secondary induccdwoltagearound the core of the furnacetransfdrmer.

My invention is therefore not limited to voltage changing transformersbut includes voltage changing connections for induction furnaces; Y

Another feature of my invention relates to the -m'eans of changing thevoltage between dili'erent'taps on either" the primary or secondarywinding: of the voltage regulating-transformer andthis feature relatesmore"particularly to the combination of a special switch in combinationwith a reactance whereby when two taps of the transformer windings areshort-circuited through the special switch the reactance will serve tolimit the current during such short-circuited'period.

Another-feature of my invention relates to thelocation of the boostertransformer secondary windingswhereby the booster has a'neutral point,and the-separate phases of a three-phase booster-are conn cted betweenthe neutral-point and one terminal of each secondarywindin'g ofthethree-phase transformer secondaries.

These and other features of my invention 'will be more-fully describedwith reference to the accompanying drawings.

Fig. 1 is a (liagrannnatic view of a threephase transformer showingconnections from it to the electrode; and also to a low voltage sourceof three-phase current. For example, 220'voltsthreephase circuit.

FigJ-2 is a View of the arran 1 ;cmcnt of the boostertransformerwindings in series with each line to the three elc ctroi'lcs of a threephase furnace and showing a diagram of the switching arrangements forvarying the voltage applied between the electrodes.

Fig. 3is a wiring diz'igrani of a threephase transformer showing specialconnections and switching arrangcmei'its for var v ing the severalvoltages induced in the windings ors'upplied by this transformer device.

Fig. 4 is a diagram of the transformer circuits and switch connectionsof a thrcc-pl'iase induction furnace.

F 5 is a diagram of the. connections of a threegp'hase" transformersystem to the electrodes of a three-phase furnace and showing thearrangement of the booster transformer connections for voltage control.

Fig. 6 is a diagram of an arrangement of secondary windings or a boostertransformer such as might be used in one of the phases star and withoutany added or substracted.

voltage of a booster transformer.

Fig. is a diagrammatic view showing in a relative way the relationshipand the amount of secondary induced voltages not only of the standardpower transformer seeondaries but also of the secondaries of the boostertransformer which when added to.

them'wo'uld give the relative value of the electrode voltages when thebooster transformer voltages are added to thosetof the standard-powertransformers, all being in star connection.

Fig. 11 shows the direction and value of the secondary voltages of athree-phase booster transformer when the direction of the inducedvoltages is opposite to that shown in Fig. 9.

' Fig. 12 illustrates the direction and value of the secondary voltageson the electrodes in case the booster Voltages are-subtracted from thetransformer voltages instead of added to them.

Fig. 13 is anotherdia'gram of phase voltages of a booster transformer;and Fig. 14 is still another diagrammatic view of the phase relationsand voltages in such a system.

Fig. 15 is a view of a modification of my invention for changing thefurnace voltage without breaking the circuit.

Referring now to Fig. 1, there is shown in this figure the wiringdiagram to illustrate the various connections which may be obtained byuse of an auto transformer in connection with an electric furnace. Forpurposes of illustration, the current supply may be considered as 220volts three-phase from suitable power transformers to supply thenecessary power for the operation of the electrodes of a three-phaseelectric furnace. vThe powersupply is indicated at 1. A three-poledouble throw switch 'is provided for connecting either of two' sets oftaps on the primary windings of the transformer with the power circuit.The switch 2 may be thrown to the left and would then connect the lines4, 7 and 10 with the power supply; or the switch 2 may be thrown to theright and then the power circuit would connect with the lines 3, 6 and 9which lead former phase 11.

to the terminals of the three phases of the auto transformer. Thetransformer is constructed with three separate windings as indicated at11, 12 and 13, and these windings are connected to them in star relationas indicated at 22 and 28. Each winding comprises a suitable number ofturns as may be required by the design of the transformer so that thepower supply may be connected between the primary connections andinduces the desired secondary voltages or the desired single turnvoltages in the windings of the separate phases. Each transformer oreach phase of the three phase transformer is provided with a set of tapsas indicated at 15, 17, 18, 19, 20, 21 and 22 for the trans- The'fourupper taps, 15, 17, 18'and 19, may be used for connection to the supplycircuit and two of these are shown, 15 and 18, leading to the oppositelugs of the double throw switch so that when the switch is thrown in onedirection to con nect with the line 10 then the tap 18 would beconnected with the supply line; and when the switch is thrown in theother direction then the tap 15 would be connected with the same line ofthe supply circuit. The other phases are constructed in the same waywith corresponding taps and with corresponding connections to theprimary supply circuit.

The auto transformer is also provided with taps which may be connectedto the electrodes and the transformer phase 11 is provided with twotaps, 20 and 21, and tap 20 is shown as connected with the centerelectrode 30. Instead of the electrode being connected to 20 it might beconnected to 21 by any suitable means with a switch or any other devicefor changing this connection.

When the double throw switch .is thrown to the left so that the taps 18,23 and 33 are connected with the 200 volt supply circuit then, forpurposes of illustration, the voltages between the electrodes might be120. In other words, if the voltage between the primary taps asindicated by the line C is 220 volts, then the voltage between thesecondary taps as indicated by the line E might be 120. The sameapproximate volt ages would hold for the other electrodes and thevoltages between all electrodes would be approximately equal. Now, ifthe end taps of the transformers. that is the taps 14,. 1 and 16, beconnected to the 220 volt power circuit then the induced voltageindicated at E, that is between taps 20 and 26, would be less than 120volts. The value of: this voltage would depend upon the number of turnsadded between the taps 18 and 15 and a suflicient number of turns mightbe added so that the electrode voltages on open circuit (that is beforethe current flows through the electrodes) would be reduced to 99 or to80 or to any other "oltage below 120 as might. be required for theoperation of the furnace.

An inbo-rinedia-te-tap, like 17,,may be pro vidod for eaclr phase, andaspecial below normal tap, like. 19 would be provided for each phase, andany of the two taps: on the primary partof a given; phase might beconneeted t'o the double throw switch for the purpose of changing fromone relatively higher voltage toione lower voltage. It is to beunderstood however, that a switch might be provided which wouldcha-i'igefrom any one to. other of the primary taps of one phase: instead: of a.double throw switch whieh only connects one or the other oi" a pain ofitaips.

RBfGIIlIlgdIOW; to. Fig. 2 I have shown here another= amnangement forthe control of voltage 015 the electrodes of a. three-electrodefurnaeeiuThe. electrodesare shown at 47, 48

and..- 49: Thneei-l'ines, 55,54; and. 53'. bringcunrenti.fiiomiithewsecondary terminals of a.three-phasetransfonmer-system; for the said electrodes; In between theelectrodes and tmainsfonme r terminals ineach phase is placedasecondaryofia: booster transformer. These secondaries a-neindicated at44; -and 46. That: is the. line. 55. coming from one terminalr-of thetransformer leads to a terminal oifi-aisecondairywinding-of the boostertrans- :nprimary-42; and'forthe-secondary 46 there is:a primary- 43.-

- The primary windings of these three booster transformers may beconnected by means of double throw switches, 62,. 63 and 64,.-betweenthe lines supplying-current to the electrodes, or in other -words,between the tln'eesecondary terminals of thet-hree-phase transformersystem supplying power. to the electrodes; These double throw switchesserve to change the direction of the induced current through the primarywindings of the booster .transformeis. Thesebooster-ironsfo'rmers may beseparate from each other, that is, each primary and secondary of abooster-may be an indi\-'idu a l transformer by itself, or the threemaybe combined as a. three-phase booster t-ransforn'ier.

In the operation ofthe-electrodes in accordance with the arrangementshown in Fig. 2 when the double throw switches are thrown 'in one;direction the, induced volt-- age inthe secondary oftheqbooster-tra-nsformer. will add; to the voltage between theelectrodes-rand when. 'the double throw switches: are thrown in theother direction thezinducedivoltage in the booster. secondary will besuch asto subtract from the electrode voltages between electrodes;

It is pointed: out. thatv these primaries .are connected in. delta.relation between :the. lines furnishing current to the electrodes, andas referred to further on,.these primaries may be connected-in eitherstar or delta. relation in accordance with the requirements. If thepower li-ansforn'ier secondaries beco-nnected in closed deltaxrelation.then these; booster transformer primaries may. be connectedas indicatedin Fig. 2. but they may. alsobe connected in star relation.asrefcrred-toelsewhere in this specification.

Fig. 3. shows a combinationthneerphase transformer system with primaryconnectionsto thepower line and with secondary connections: to.'theelectrodes. ,fllhef three phaseshere shown are connected as al totransformers, The primary windingsifare pro vided with separate. coils[on sets, of ooil s so that a portiomofthe-pnimary maybe. opierated in;either series o-npar Fuelrelation with another similar portionof thesamci pri niary. This will.be. described. withregard to the left-handwinding. The. thljeelpower lines which supply currenttortheauto-transformer are shown at 92,. 9.3,arid: 94..-The primary has.two. separate-setsofQcoiIl's; one

end of one being shownat89.andtoneendlof the other at.-83,.andtheopposite endsat. 86 and respectively. These windings may be thrownin.- senies .by. throwing. the switch- 95 down and they. may be thrown:inlliaiallelby throwing.; the switch: 95 up The. {other .tw phases areprovided withaisimilar arrange ment of coils and switches, the.switchesheing shown at-.95, and.9.7.. 7 The eonnectionstothe. threeelectrodes of the furnace are: shown. at 74,.75- and. 76.; ..The othertaps, 79, 78 .andi'l' 'i maybe connected with the electrodes instead ofthe higher voltage taps .last mentioned. The three separate phases-areshown at. 71,. 72pand 73 and are here shown connected instar.relationi...

Fig. 4 isra transformer system which. may

include a single: turnsmo-ndary heating circuit which mightbe. an.induction furnace. The transformer system is connected by means-ofaswitch 1111 to. a power supply. cireuit indicated at-112..Thesystei'riis pro.- vided. with two.- transformer, cores, 121. and 122,which may seiwe tooperate inopcndelta relation. Two primary windingsareshown at 101 and. 102.. Additional. primary winldings are shownat'115 andll6and. these may be. operated in eithen series. or.parallelrelationcto each other-by. means of theswitch L19, and.- t-heymay. be. Connected through the -siw.itcl1.11.=3 tothezother. portionof.tliecoil 101.. The windings .101 .andl 1 Q2.may be'c'onnested inopendelta. nelationto the. power duced secondary voltage in thesecondary circuit 123 by means of the switch 119. When the switch 119throws the two coils 115 and 116 in parallel then the number of turns ofwinding between the line 105 and the line 108 will be less than when thetwo coils 115 and 116 are thrown in series by throwing the switch 119 inthe opposite direction. In this way the single turn voltage induced inthe primary winding may be increased or diminished. hen it is desired tolower the single turn voltage of the primary and therefore of thesecondary more turns would be put in circuit between the conductors105'and 108.

The single turn induced voltagein the other secondary 124 may beregulated and controlled in thesaine way as just described. The voltageineither phase may be regulated and controlled independently of that inthe other phase.

l-Vhen the two phases. that is the two sepa rate primary windings of thetransformers, are connected in open delta as would be the case when theswitches 119 and 120-aiid 106 and 111 are closed, then a certain singleturn volta e would be induced in each phase, and then by opening theswitch 106 but leaving the other switches closed, the two primarieswould be thrown in series with each other and therefore the total numberof turns between two conductors like the conductors 108 and 109 would'be doubled and the single turn voltage correspondingly reduced.

Referring now'to Fig. 5 I have shown'here another system of transformerconnections and the diagram in this figure represents the threeelectrodes of an electric furnace shown at 125, 126 and 127 connectedthrough reactance coils shown at 133,132 and 131 to the secondaryterminals of three transformer secondaries. These power transformers arerepresented in the diagram at 135, 134 and 136. These transformersecondaries may be of volts each for example. YVhen they are connectedin star relation the voltage between electrodes on open circuit would beroughly 121 volts (70X 1.73). This .diagram in Fig. 5 shows a secondaryof a booster transformer connected between one end of each powertransformer and the neutral point of the secondary system. These boostersecondaries are indicated at 133, 137 and 139 and they are connectedtogether in star relation. Each booster secondary might furnish 12 voltsfor example in addition to the 70 volts of each power transformersecondary and then the voltage between electrodes would be approximately141 "olts (82XL73). Referring to Figs. 9 and 10, 1f the powertransformers were connected in 5 star without the booster voltage beingadded the diagram of the voltages of the three transformer secondarieswould be somewhat like the diagram shown in Fig. 9; that is the voltageof the secondary 134- would be represented roughly by the line 181 andthe voltages of the other two secondaries 135 and 136 by the lines 182and 183. Now if the booster transformer secondaries are in sorted asshown in Fig. 5 then the voltages of the separate phases and separatesecondaries w'ould'be roughly as indicated in Fig. 10. That is thevoltage of the secondary 134 of the power transformer which would be 70volts is represented by the line 184, and the voltage of the boostertransformer 137 is represented by the line 187 and if these two he addedtogether the sum of 70 "olts and the 12 volts would'be roughly 82 voltsbetween the neutral point and the electrode. It is understood that thisdiagram does not take account of the disturbance of the phase relationsresulting from the passage of current through the reactances in circuit.Thevoltages in the other'secondaries would be indicated in Fig. 10as'already mentioned for the secondaries 134 and 137.

The booster transformer secondaries 137, 138 and 139 could beshort-circuited by means of'a knife switch or other suitable switch sothat the transformers would be connected directly together in'star ontheir secondary side without any effectfrom the booster .transformer.When the secondaries of theboos'te'rtransformers are short-circuited theprimaries must of course be shortcircuited or disconnected in such amanner as not to short-circuit the power transformer through thesecondary windings. Instead of short-circuitingthe secondaries theprimaries could be disconnected from the lines which supply the inducingcurrent and they could be short-circuited instead of the secondarywindings being short-circui'ted but in such event there is anincreasedloss due to the passage of the currentbetween the neutral pointof the system on the secondary side through the booster secondaries sothat in certain cases it may be desirable in order to increase theelficiency to use switches on both the primary andsecondary windings ofthe booster transformer system. r

The direction of the induced voltage in the secondary transformerwindings may be reversed by reversing the-direction of the connection ofthe primary windings between the lines. For example, referring to Fig.7; if the primary of the-booster transformer 1s 1ndieated at 162 and thethree-phase circuit lincs at 165, 166 and 167, then the primary winding162 may be connected between the lines 165 and 166 in either directionby reversing the switch 164. For example, when the switch 164 is thrownup then the terminal 163 of the primary connects with the line 165 butwhen the switch 164 is thrown down then the same terminal 163 isconnected with the other line 166 and at the same time this doublethrow, double pole switch reverses the connection of the other terminal162. In other words, this Fig. 7 shows a diagram of the change in thedirection of the current through the primary winding of a boostertransformer.

Referring now back to Fig. 5, there is shown the three booster primariesat 140, 1 11 and 142 and these are connected together in star relationwith each otlrer and with the three lines connecting with theelectrodes. For example, the power transformers supply 140 volts to theelectrodes and the ,pri inaries of the booster transformers areconnected between :these three lines shown at 128, -129 and 130. I haveshown the connection between these lines and the three transformersindicating that the number of turns of-each primary may be varied sothat the line voltage applied to these primaries may be regulated andcontrolled as desired. Fpr

example, vin the diagram shown in this Fig.

5 whenthe voltage betweenthe electrodes is lowered then it may bedesirable to change the number :of turns on the primaries of the boostertransformers so as to regulate the amount of the secondary voltage ofthe booster transformers.

.Although I have shown the booster transformer primaries connected in:star it is understood that they may be connected in delta between thelines or they .may be -thrown from star -to delta in order to change thesecondary voltage of the booster transformer or their connections toeach other and 'to the lines which may be controlled and regulated inany manner I have shown in the sev eral figures in the drawings.

\Vhen it is desired to have the secondary booster voltage buck the powertransformer voltage then I may reverse the direction of each of theprimary windings so that the 12 volts, for example, instead of beingadded to -the volts of each phase of the power transformers would besubtracted from that 70 volts with the result that the voltage betweenthe neutral point and each electrode would be approximately 58 volts andthe electrode voltage would then be approximately 101 volts instead of140 volts when the booster transformer voltages were added to the powertransformer secondary voltages. This relation of secondary voltagesbetween electrodes is :further show-n diagrammatically in Fig. 12. Thenet voltage between the neutralpoint and the electrodes is indicated bythe lines 193, 194, 195. That is, instead'of-the voltage correspondingto the line 181 in Fig. 9 the line 193 is shorter by the amount-of thevoltage induced in-the booster transformer but induced in the directionopposte to that of the secondarypower transformer voltage 193. Thevoltages of the other phases are shown at 194 and 195 respectively. Thediagram of the primary windings is then represented in Fig. 11 where thevoltage in the primary 142 is represented by the line 190 and beforereversing the directionof connection of this particular phase thevoltage would be represented by the line 183 in Fig. 9.

I have shown inFig. 8 a diagram of connections for changing the boosterprimaries from star to delta. The three primary windings are indicatedzit-170, 171 and 172. The double throw switch 176 serves to connectthese separate windings in either star relation by connecting themtogether by throwing the switch 176 down to the point 17 7, or if theswitch 176 is thrown up it connects'the prnnaries in delta relation withthe linesfl78, 17.9 and 180. I

When this switch 173 is connected with the line.1i74 and the threephases are connected in star through the switch 176 then the transformerwinding 170 is in circuit but if this transformer winding 1'70 is-'disconnected by opening the switch 173 and closing it to the point of '175,then 'thisparticular phase would be short-circuited. The other twophases, 171 and -172 ,-m'ay be likewise provided with such a switching"arran-gement so that they can be short-circuited. That is, if it isdesiredto neither add to nor subtract from the"powertransformer voltagethese booster transformer primaries may be-shor t-circuited in themanner just described so that there is no voltage induced in them andthen the booster transformer secondariesmay likewise be shortcircuite din order tosave thel'oss of power from the current flowing through themin the operation ofthe'jpo'wer transformers.

I have shown in Fig. "6 one arrangement of the secondarywindings of thebooster transformer. I have shown here two secondary coils havingterminals '151, 152, 153 and 154. These coils .migbt represent singleturns. They might be, for example, 6 "olts each with certain primaryconnections to give this secondary induced voltage. They may beconnected in series so as to give a total of 12 volts, or they may beconnected in parallel 'to .give greater capacity at only 6 volts. Stillagain, the induced voltage may be varied by means of the primaryconnections of the booster transformer.

With further reference to 'Fig. 3, I have shown three single turncircuits which represent diagrammatically the secondary cir cuits of aninduction furnace, one for each phase. These are shown "at 74", Pand=76. I have done this merely to indicate that the voltage regulatingsystem shown and described with reference to Fig. 3 may .beused for theregulation and control of the voltages in the three separate circuits ofthe three phase induction furnace in the same manner Hti.

llt

as has been described for the regulation of the voltages in theelectrode circuits con nected with the taps 74, and 76. It is furtherunderstood that the operation of the booster transformer system shown inFig. 2 may be in accordance with that described in other figures. Thatis, the primaries may be connected as shown in Fig. 8, for example, orin any other way illustrated or described herein.

In Fig. 15 I have shown one means of changing connections betweendifferent taps and a'line. In this figure I have shown a transformerwinding which may be either primary or secondary at 210. This winding210 is provided with a suitable series of taps like the taps 203 and 204connecting with a part of the winding shown at 202, that is, connectingwith different coils of this part of the winding. A switch 209 isprovided and this switch has two connecting conductors, 206 and 208.This switch is mounted on a suitable pin so that it may revolve aboutthis pin by means of the handle 209 and connect with different taps likethat shown at 205. The two terminals 206 and 208 are connected togetherby means of a suitable reactance 207 and this reactance may in turn beconnected with the line which it is desired to connect with any giventap. In the operation of this switch when it is shifted between the tapsof a transformer winding if two taps are shortcircuited they are shortcircuited through the reactance 207 and this may be sufficienttopreventany undesired heating as a result of short-circuiting twodifferent coils of the transformer winding. The switch may thus beshifted between any of the taps and when left in connection with any onetap it is in such position that both the switch terminals 200 and 208will rest on the same tap, as for example, 205, so that therewill be noinjurious short-circuiting of the winding.

Referring to Fig. 13 and Fig. 14, I have shown here the relativedirections of the induced voltages in a three-phase booster transformersystem when the primaries are connected in delta and the secondaries instar. Thus, if the line 196 represents the direction of the primaryinduced voltage then the secondary induced voltage for the correspondingphase would be along the line 199 of Fig. 14 although opposite indirection. These two diagrams in Fig. 13 and Fig. 14 do not show thevoltage values which might be obtained in such a system.

It is understood also that a switch like the switch 173-in Fig. 8 may beused in connection with the secondary windings. For example, such aswitch might be provided in connection with the secondaries like that at137 in Fig. 5 so that when the primaries are disconnected from the lineand short circuited, the secondaries may also be short circuited ifdesired.

It is understood that the improvements which I have described in thisapplication may be combined in various ways without getting away fromthe invention.

In order that the n'iethod of using this apparatus of this inventioncannot be misunderstood, I will describe how, for example, the apparatusshown in Fig. 5 may be used for melting and refining basic steel, thatis for melting a charge of steel scrap in a basic lined hearth andrefining or treat inc the molten steel after it is melted. The co (1steel scrap would be charged into a furnace into which the threeelectrodes 125,

126 and 12:? enter. The transformers and booster apparatus would beconnected to give, for example, 120 volts between electrodes for meltingthe charge and heating the metal. This voltage between electrodes mightbe obtained by the following combination. The three power transformershave their secondaries connected in star, one terminal of each secondarybeing connected to the neutral point. The neutral point may or may notbe grounded. The booster seeondarics are placed one in series with eachpower transformer secondary. If the power transformer secondary be 70volts and the booster normally 12 volts, then in order to use the 120volts between electrodes, the booster transformer secondaries would beshort circuited and the power transformers connected in star would givethe 120 volts between electrodes, or 121 volts more nearly. Then if alower voltage is desired for finishing the heat a voltage betweenelectrodes of approximately 100 volts open circuit could be used. Thisvoltage would be obtained by connecting the booster transformerprimaries to the power transformer secondary terminals giving 120 voltsbetween terminals and the proper taps on the booster primaries would beselected to give about 12 volts which voltage would buck the 70 volts ofeach power transformer,-giving a net voltage of about 58 volts betweeneach electrode and the neutral or approximately 100 volts betweenelectrodes. The change of voltage may be accomplished by a double throwswitch as indicated in Fig. 8 operating on the booster primaries. henoperating at a voltage of 120 between electrodes the switch would shortcircuit the primaries of the boosters; and at the same time thesecondaries could be also short circuited by suitable switches or by asingle three pole switch. Then when 100 volts is wanted the primarybooster switch would be thrown the other way and would so connect thebooster primaries to the 120 volt 3 phase.

circuit as to produce a voltage of 12 volts 311 each secondary to buckthe 70 volts.

In case the power transformers are C(Jll nected as shown in Fig. 5 sothatthe booster secondaries are between them and the neutral point thenthe booster l'n-iinarics; can be energized from the power transformersand a single double pole double throw switch used for each boosterprimary,so that the booster primaries would not be subject to thevoltage change of the electrodes. The arrangemei'it in Fig. 2 shows this'kind (it a connection with a standard low voltage power. circuit wherethe booster primaries are connected back of, that is on the power supplyside of the-eleotrm'lcst Itzis understood "that the voltage may bechanged at-any time'desired during the metallurgical-process. -F orexample it maybe desired tostart witlrahigh voltage and use it until the--bat-hiiand 'charge become sufiiciently'hot-to necessitate pullingoutthe arcs in order to ilo-Wer the development of energy in the arcs.This pulling out -of therescm poses the walls of the furnaceunnecessarily to -the -heatrof the long arcs and the xoltage may bechangedbefore the-arcs have tobe pulled out and -the voltz'ige m'aybe'changed so as to maintain the powerhigh or :low and at same time keepthe arcs withiii approximately constant. length.

:It is also understood that my present invention maybe applied to aninduction fur na'ce or 'torother types of resistance furnaces and Izrlsothat-the change from ,one connectioxi of taps to another may be made byany suitable switching arrangement or means of changingconneotions.=However, the modi-- ficatio'n of vmy invention whereby the appliedvoltage can be changed Without cutting off the .power from the furnace,that is by using the device shown in Fig. 1'5, and

this may --be used either in an induction fnrnace or in ia-n'lectrodefurnace.

VV-hat :Lclaim is: i

1. In combination with the electrodes of an electric furnace atransformer system comprising a plurality of secondary windingsconnected together :in series relation, a. conductor for carrying thecurrent from said secondary :windin-gs to an electrode, and means forregulating the relative value and direction of induced voltage-in theseparate secondary windings for controlling the voltage between'theouter :e'ndsof the two windings when connected in series.

2. In combination with electrodes of an electric furnace, a secondarytransformer winding connected in series with an electrode, "a-.sep-arate secondary transformer winding also in series with said firstsecondary, and means of inducing voltage in thezseparate secondarieswhereby the smaller secondary voltage is either added to or subtractedfrom, that is boosts-or bucks the voltage of the main secondary.

3. A system, for controlling the voltage between the electrodes in anelectric furnace comprising a main transformer and a booster transformerwith their secondary windings in series and means for control lingrelative direction and value of the induced voltage whereby the smallersecond ary voltage may be added to or subtracted from the largervoltage.

4. The con'ibination with an electric fur-v nucc of means for supplyingalternating cur-' rent thereto at varying voltages, said meanscomprisinga plurality of power transform ershaving their secondariesconnectedwith the furnace terminals and a booster transformer in seriesbetween each power-transformer and a furnace terminal, and means forregulating the direction and value of the induced" voltage in thebooster secondary.

5. The combination with an electr-ic furmice of means for supplyingalternating current thereto, and means for connecting sec- {ions of atransformer windingtogetherin' series 'or parallel relation and means;fo r.- (ionnecting said sections inserieswith another section forvarying the-inducedvoltage of Lhetransformer, i

6. In combination with an electric furnace, a source ofpoly-phasealternatingIcurrent power for supplying current to theterminals of said furnace,-and a booster transformer having a secondarywindingin series between one terminal of each-,phase of the fur-J naceand a corresponding phase ofthe sup ply circuit and means for.controlling; the relative direction and va-lueiof the seoondary voltagein each phase of the boostertransformer.

7. In combination with-an electriczfurnace, a source of alternatingcurrent power for supplying current to the terminalsiof sa'id furnace, abooster transformer having-a secondary winding -in series between thefurnace terminal and the power supiplygiaprimary winding for saidbooster transformer, and a switch for controlling the direction ofcurrent flow through the primary of said booster transforme e 8.Iii-combination with an electric furnace, a source of three phasealternating current, a three .phase booster transformer havingitssecondary windings connected in star betwecn a neutral point -and thethree-secondary terminals of three power transformers, the othersecondary -terminals .of said power transformers leading to the furnaceterminals and means off-controlling thedirection and valueof thesecondary' booster voltages.

9. In combination with an electric furnace, a source :ofthrce phasealternating current for supplying current -to'-the furnace terminals, abooster transformer having a sec--. ondary in series between eachfurnace terminal and the corresponding phase of the power supply andmeans of connecting the booster primaries in star or delta relation tochange the booster secondary voltage 10. In combination, an electricfurnace, a transformer system having taps for supplying differentvoltages to the furnace terminals, a switch mounted to connect withdifferent taps of the same phase, and means for limiting the shortcircuit current between two taps during the shifting of the switch fromone tap to another.

11. In combination with an electric furnace, a transformer having tapsfor different voltages, a switch mounted to change connection from onetap to an adjacent one, said switch comprising a current limiting devicewhich operates to limit the short circuitcurrent between two taps duringthe period when they are short circuited thru the switch connections inshifting the switch.

12. In combination with an electric furnace, a transformer havin taps, aswitch for changing connections from one tap to another without breakingthe circuit to the furnace, said switch being mounted to make connectionwith two taps at the same time during movement from one to another, anda current limiting device in combination with said switch to limit theshort circuit current thru the part of the winding short-circuitedduring movement of said switch.

13. The method of operating an electric furnace which method consists inconnecting a winding of a transformer in series with a terminal of theelectric furnace and regulating the circuit connections to control thedirection and amount of the induced voltage in combination with thevoltage of the supply circuit.

14. In combination with an electric arc furnace for the manufacture ofiron or steel, said furnace requiring different voltages on theelectrodes for its operation, a transforiner, a winding thereon, aseries of taps on said winding for inducing the desired voltage to beapplied to said electrodes, and a switch for changing from one voltageto another without breaking the circuit supplying current to theelectrodes or interruptmg the are.

15. In combination with an electric furnace having arcing electrodes, atransformer supplying current to the electrodes and another transformerwinding in series between an electrode and the transformer firstmentioned, and a primary winding for the series transformer, and switchmeans for connecting this primary to the circuit between the firstmentioned transformer and the electrodes when thrown in one directionand for short circuiting the primary winding of the series transformerwhen thrown in another direction.

16. In combination with an electric furnace having arcing electrodes, athree phase transformer for supplying power to the furnace and a secondtransformer having a secondary winding in series with each electrode andhaving a primary which can be shortcircuited by switch means and whichcan be connected to the electrode side of the series transformersecondary winding so as to cause the voltage thereof to oppose that ofthe power transformer.

In witness whereof, I hereunto subscribe my name this 15th day of May,A. D. 1923.

ALBERT E. GREENE.

